Tubular Coupling Assembly With Modified Buttress Thread

ABSTRACT

Tubular coupling assembly with modified buttress thread includes a coupling member to couple two pin connections. The coupling member includes an outer surface and an inner surface opposite the outer surface, which can seal to surfaces of the two pin connections. The inner surface includes a first tapered axial portion extending from a first end of the coupling member towards a center of the coupling member. The inner surface includes a second tapered axial portion extending from a second end of the coupling member towards the center of the coupling member. The coupling member includes a shoulder portion connecting the first tapered axial portion and the second tapered axial portion. Regions of the shoulder portion that connect to the first tapered axial portion and to the second tapered axial portion have respective concave shapes to couple to respective convex shapes on each of the two pin connections.

TECHNICAL FIELD

This disclosure relates to a tubular coupling assembly, for example, a coupling member coupled to two pins such as two tubulars, to form sealed assemblies.

BACKGROUND

Wellbore tubulars can be axially coupled, end-to-end, using threaded joints. One technique to couple two tubulars is using buttress threads and a hollow coupling. A first end of a first tubular has a thread profile on a tapering outer surface. A first end of the second tubular also has a thread profile on a tapering outer surface. The coupling is a hollow member that has complimentary internal threads on its inner surface. The inner surface of the coupling also tapers from respective ends of the coupling towards a center of the coupling. The threads are formed on the tapered portions. An unthreaded shoulder joins the two tapered portions of the coupling. The threaded end of the first tubular and the threaded end of the second tubular are screwed into respective ends of the coupling. The thread profile is a buttress thread that joins the two tubulars and also seals the outer surfaces of the two tubulars to the inner surface of the coupling.

SUMMARY

This specification describes technologies relating to a tubular coupling assembly with modified buttress thread.

The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a cross-section of a coupling member joining two wellbore tubulars.

FIG. 2 is a schematic view of a cross-section of the coupling member and one of the two wellbore tubulars.

FIG. 3 is a schematic view of a seal.

FIG. 4 is a schematic view of a seal groove to receive the seal of FIG. 3 .

Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

This disclosure describes a coupling assembly (i.e., a combination of a coupling member and two tubulars) that solves a challenge of leakage into annuli in wellbores, for example, due to poor zonal isolation post a cementing stage. Such poor zonal isolation can lead to ingress of hydrocarbon between intermediate and/or outer casing strings. The coupling assembly described here provides improvement in long term well integrity by improving the barrier element. The coupling assembly can be used as a gas tight connection for large diameter tubulars in shallow gas intervals or as production string for gas wells, oil wells with high GOR oil and gas-lift applications. The coupling assembly can form a hybrid or metal-to-metal (or both) connection with buttress thread form and pitch and can be used in API or proprietary connections.

FIG. 1 is a schematic view of a cross-section of a coupling member 100 joining two wellbore tubulars (e.g., a first tubular 102 and a second tubular 104, also called pin connections). The coupling member 100 has an outer surface 116 and an inner surface 118 opposite the outer surface 116. The inner surface 118 is configured to seal to surfaces of the two pin connections, namely, the first tubular 102 and the second tubular 104. The inner surface 118 includes a first tapered axial portion 120 extending from a first end 122 of the coupling member 100 towards a center of the coupling member 100. The inner surface 118 also includes a second tapered axial portion 124 extending from a second end 126 of the coupling member 100 towards the center of the coupling member 100. The inner surface 118 further includes a shoulder portion 106 connecting the first tapered axial portion 120 and the second tapered axial portion 124. Regions of the shoulder portion 106 that connect to the first tapered axial portion 120 and to the second tapered axial portion 124 have respective concave shapes 128 that couple to respective convex shapes 110 on each of the two pin connections, i.e., on each of the first tubular 102 and the second tubular 104. The inner surface 118 forms a metal-to-metal seal 108 with the surfaces of the two pin connections. The seal face formed by the coupling member 108 is not limited to a tapered face to tapered face, metal-to-metal seal with the tubulars. Other seal face combinations can be used provided the seal face does not induce additional stress to the connection during make up or jeopardizes the integrity of the connection seal during cyclic loading.

In some implementations, each of the first tapered axial portion 120 and the second tapered axial portion 124 can include a respective pocket (e.g., pocket 114) that can accommodate excessive dope (i.e., a sealant used with threaded pipes to create a seal) when the coupling member 100 is coupled to the two pin connections, i.e., the two tubulars. In some implementations, the pocket 114 can accommodate excessive dope applied during make-up process and reduce the risk of humping and leaking connection. The pocket 114 can be included in the pin connection around the initial partial or unengaged threads such that at final make-up (i.e., contact with the concave shoulder), there is a pocket or a space in the connection to accommodate the excess dope during make-up process. The pocket 114 formed by the pin is not limited to using the overlap between the plane of end of power tight to the plane of hand tight of a standard buttress with no threads on the pin to create a gap. Alternatively, the pocket 114 can be included in the coupling member 100 or both connections (tubulars and the coupling member 100) in the initial partial or unengaged threads zone. The dimension of the pocket 114, whether in the pin or the coupling member or both, should have minimum impact on the compression capacity of the connection at final make up.

FIG. 2 is a schematic view of a cross-section of the coupling member 100 and one of the two wellbore tubulars. The metal-to-metal seal 108 between the sealing face of the seal ring in the box connection (i.e., the coupling member 100) and the contact with the seal face in the connection pin (i.e., each tubular) forms a gas-tight metal-to-metal seal. The metal-to-metal seal 108 faces uses controlled make up process to conform the metal and achieve pressure barrier which allows for contact and sealing capabilities without plastic deformation of the pin face. FIG. 2 shows the internal diameter 202 of one of the pin connections, e.g., the first tubular 102. The metal-to-metal seal 108 is formed where the thread profile of the tapered axial portion (e.g., the first tapered axial portion 120) ends and the concave shoulder 200 begins. The positive shoulder 200 serves as an indication of full thread travel of the pin connection. The shoulder 200 can be formed by machining a shoulder in the buttress thread of the coupling member 100 to replace the current unengaged thread section between the two tubulars post make-up.

In some implementations, the dimension of the shoulder 200 is such that the middle section of the concave shape, which will have the most stress in the shoulder 200, has sufficient thickness to withstand compression loads without plastic deformation of the shoulder 200. Ends of the shoulder 200 are comparatively thinner and trimmed compared to the middle of the shoulder 200. Such design prevents easy chipping during connection make-up or well intervention. Due to the design described here, additional incremental turn after shoulder contact of the pin connection imposes sufficient compressive load on the metal-to-metal seal 108 to ensure a gas-tight seal integrity without plastic deformation of the pin nose. Inclusion of the load shoulder 200 delivers a flush inner diameter in the buttress connection. Also, the base triangle correlates with the shoulder contact of the pin with the box connection and make-up torque ranges can be provided for different connections depending on the grade and weight. This is in contrast to the current reliance on average torque to reach the base triangle during make-up process.

The use of the metal-to-metal sealing system in the buttress connection eliminates limitations with interference or common resilient seals used in some modified buttress connections. Examples of failures that the disclosed coupling member eliminates includes (i) temperature degradation of interference or resilient seal; (ii) dynamic failure of interference or resilient seal under cyclic pressure especially when used as a production string; (iii) seal failure under compression load; (iv) chemical degradation of resilient seal or interference seal.

FIG. 3 is a schematic view of seal 300. In some implementations, the seal 300 can be used as a secondary sealing mechanism to improve the leak performance of the buttress thread with reference to FIGS. 1 and 2 or as a tertiary seal in implementations that include thread interference seal. In the implementations described earlier, the shoulder portion 106 (FIG. 1 ) is made of metal. In the implementation described with reference to FIG. 3 , the coupling member 100 can additionally include the seal 300, which can be made of a polymeric or elastomeric material 302. The material 302 is a non-water swellable material meaning that it does not swell in the presence of water. In some implementations, a hydrocarbon swellable polymeric or elastomeric material can be used such that the seal 300 is not expected to deteriorate over time in water-based environment or when in contact with hydrocarbon. The volumetric strain of the hydrocarbon swellable seal should be within dimensional tolerance such that interference is still maintained such that additional stress or hoop stress is not imposed to cause inner diameter restriction or drift challenges, thereby compromising the secondary or tertiary seal integrity depending on the application.

The coupling member 100 can include a seal ring groove 301 (shown in FIG. 4 ) that is configured to receive the seal 300. The dimension at the base of the seal 300 is slightly less or equal in dimension to the seal ring groove to allow for ease of placement of the seal 300 in the groove and dimension of the seal 300 will depend on the size of the tubulars against which the seal 300 seals. The thread groove where the seal 300 is placed near the shoulder 200 will have sufficient tolerances to have interference fit with or without the volumetric strain of the hydrocarbon swellable seal 300. The specific dimensions of the thread groove are in accordance with the size of the tubulars, and the thread groove size and shape used. The thread groove can be rectangular in shape, but need not be. The base dimension can match or be slightly less than the base dimension of the hybrid seal ring. Or, where similar shape as the seal ring is used, the top dimension of the groove can be less. In all, at final make-up, the seal 300 can be compressed into the groove to the approximate dimension of the groove and can seal effectively against the surface of the coupling member 100. Even if volumetric strain occurs as a result of hydrocarbon ingress, there is still sufficient compression in the seal ring to form a seal. In some implementations, the seal ring groove can be placed in the runout thread zone. The groove dimension where the seal 300 is placed in the runout thread depends on the wall thickness in the zone and includes sufficient tolerance to have interference fit with or without the volumetric strain of the hydrocarbon swellable seal ring where applicable.

The combination of metal within the seal 300 improves the stability, strength and temperature limit of the seal. In some implementations, the seal 300 can encapsulate a metallic strip 304. Together with the metallic strip 304, the seal 300 forms an inverted trapezoidal shape. The materials (e.g., the polymeric or elastomeric materials, the metal for the metallic strip, and other materials used to make parts of the seal 300) can be selected such that there is a compatibility between the seal material and the metallic material that reduces risk of shear failure of the seal 300 during make-up process. Depending on the type of material and the seal contact areas, the shape of the seal need not be an inverted trapezoid.

The coupling member 100 described in this disclosure can be used in a top-hole application for tubulars having diameters greater than 16 inches or deeper hole applications for tubulars having diameters less than 13⅜ inches (or both). The former can utilize a hybrid seal (e.g., the seal 300) as a secondary sealing mechanism. The latter can be used using the metal-to-metal seal. The modified buttress connection with a metal-to-metal seal can also be used as a gas-tight connection in shallow gas intervals or where there exists a risk of gas migration between intermediate casing and the wellbore surface.

In sum, implementations of the subject matter can reduce erosion risk of the connection post make-up process and deployment. The approach involves reducing turbulence in the coupling section between two ends of the tubulars post connection make-up. Elimination of the unengaged thread section in the coupling and ensuring a flushed ID with the shoulder reduces the risk of turbulence in the area while drilling the next hole section or during production if used as a production string. The approach also limits the degree of abrasion in the coupling in this section to wear and ultimately connection leak. Thus, particular implementations of the subject matter have been described. Other implementations are within the scope of the following claims. 

1. A coupling member configured to couple two pin connections, the coupling member comprising: an outer surface; an inner surface opposite the outer surface, the inner surface configured to seal to surfaces of the two pin connections, the inner surface comprising: a first tapered axial portion extending from a first end of the coupling member towards a center of the coupling member, a second tapered axial portion extending from a second end of the coupling member towards the center of the coupling member, and a shoulder portion connecting the first tapered axial portion and the second tapered axial portion, wherein regions of the shoulder portion that connect to the first tapered axial portion and to the second tapered axial portion have respective concave shapes configured to couple to respective convex shapes on each of the two pin connections.
 2. The coupling member of claim 1, wherein the inner surface is configured to form a metal-to-metal seal with the surfaces of the two pin connections.
 3. The coupling member of claim 1, wherein each of the first tapered axial portion and the second tapered axial portion comprises a respective pocket configured to accommodate excessive dope applied when the coupling member is coupled to the two pin connections.
 4. The coupling member of claim 1, wherein the first tapered axial portion and the second tapered axial portion comprise respective buttress threads to couple to respective complimentary buttress threads of the two pin connections.
 5. The coupling member of claim 1, wherein the shoulder portion is made of a metal.
 6. The coupling member of claim 1, further comprising a sealing element made of a polymeric or elastomeric material, wherein the coupling member comprises a seal ring groove configured to receive the sealing element.
 7. The coupling member of claim 6, wherein the sealing element encapsulates a metallic strip.
 8. The coupling member of claim 6, wherein the polymeric or elastomeric material does not swell in a presence of water.
 9. The coupling member of claim 6, wherein the sealing element has an inverted trapezoidal shape.
 10. The coupling member of claim 6, wherein the seal ring groove is formed in the shoulder portion of the coupling member.
 11. A wellbore completion comprising: a mill end tubular comprising an end; a field end tubular comprising an end; and a coupling member configured to couple the mill end tubular and the field end tubular, the coupling member comprising: an outer surface; an inner surface opposite the outer surface, the inner surface configured to seal to end of the mill end tubular and the end of the field end tubular, the inner surface comprising: a first tapered axial portion extending from a first end of the coupling member towards a center of the coupling member, a second tapered axial portion extending from a second end of the coupling member towards the center of the coupling member, and a shoulder portion connecting the first tapered axial portion and the second tapered axial portion, wherein regions of the shoulder portion that connect to the first tapered axial portion and to the second tapered axial portion have respective concave shapes configured to couple to respective convex shapes on the end of the mill end tubular and the end of the field end tubular.
 12. The coupling member of claim 11, wherein the first tapered axial portion and the second tapered axial portion comprise respective buttress threads to couple to respective complimentary buttress threads of the two pin connections.
 13. The coupling member of claim 11, wherein the shoulder portion is made of a metal.
 14. The coupling member of claim 11, further comprising a sealing element made of a polymeric or elastomeric material, wherein the coupling member comprises a seal ring groove configured to receive the sealing element.
 15. The coupling member of claim 14, wherein the sealing element encapsulates a metallic strip. 